The invention relates in general to heated tip fuel injectors with internal heaters and, in particular, to a method of enhancing heat transfer from the internal heater to the fuel in a heated tip fuel injector.
It has been recognized that preheating of the fuel during cold starting will reduce hydrocarbon emissions caused by incomplete fuel vaporization during cold starts. Heated tip fuel injectors are known and described in, for example, copending applications Ser. Nos. 09/088,126 now U.S. Pat. No. 6,109,543 and Ser. No. 09/088,127 now U.S. Pat. No. 6,102,303 referenced above. While those patent applications generally describe enhancing the heat transfer from the heater to the fuel, more efficient heat transfer mechanisms and methods are needed to further reduce emissions.
It is an object of the present invention to provide a method of enhancing heat transfer from the internal heater to the fuel in a heated tip fuel injector.
This and other objects of the invention are achieved by a method of heating fuel comprising providing a fuel injector having an internal heater and a reciprocable needle valve; providing fuel to the fuel injector; passing the fuel through at least one flow-disturbing element; and heating the fuel.
The method further comprises exiting the fuel from the fuel injector.
In one embodiment of the inventive method, the at least one flow disturbing element reciprocates with the needle valve.
In another embodiment of the inventive method, the at least one flow disturbing element is stationary with respect to the needle valve.
In a broad aspect, the passing step includes passing the fuel through a first opening in the flow disturbing element and then passing the fuel through a second opening in the flow disturbing element wherein the second opening is offset from the first opening.
Preferably, the passing step includes passing the fuel through a first plurality of openings in the flow disturbing element and then passing the fuel through a second plurality of openings in the flow disturbing element.
In a preferred embodiment, the first plurality of openings are offset from the second plurality of openings such that, when viewed in a longitudinal direction of the injector, there is substantially no overlap between the first and second plurality of openings.
More preferably, the passing step includes passing the fuel through a first pair of opposed openings in a first disk, through an opening in a second disk, and then through second and third pairs of opposed openings in a third disk.
Most preferably, when viewed in a longitudinal direction of the fuel injector, the first pair of opposed openings in the first disk do not substantially overlap the second and third pair of opposed openings in the third disk.
In another aspect of the method of the invention, the passing step includes creating a swirl flow component in the fuel. Preferably, the step of creating a swirl component includes creating a circumferential flow component in the fuel by directing the fuel through at least one arc-shaped opening in the flow-disturbing element. Most preferably, the step of creating a circumferential flow component in the fuel includes directing the fuel through six arc-shaped openings in the flow-disturbing element.
In one embodiment, the step of directing the fuel includes directing the fuel in one direction through three of the arc-shaped openings and directing the fuel in an opposite direction through the other three of the arc-shaped openings.
Preferably, three of the arc-shaped openings are substantially equal in size and spaced substantially uniformly in the flow disturbing element and the other three arc-shaped openings are substantially equal in size and spaced substantially uniformly in the flow disturbing element.
More preferably, three of the arc-shaped openings are located further from a center of the flow-disturbing element than the other three arc-shaped openings.
In one embodiment, when the needle valve reciprocates to a closed position, the flow-disturbing element rests substantially on a top of the internal heater. In another embodiment, when the needle valve reciprocates to a closed position, there is a gap between the flow disturbing element and a top of the internal heater.